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APS-C sensor issues

Whatever the focal length says on the lens, with an APS-C sensor camera, you have to multiply it by 1.5x (for SONY) to get the effective frame size of what your would see on a Full Frame camera.

Basically, the 17-50mm f/2.8 lens on an APS-C camera turns out about the same images as the 28-75mm f/2.8 lens on the Full Frame.

In a nutshell, here is the image circle from the back of the lens and how it relates to the two different sensors.

Because the APS-C only sees a smaller part of the image circle, it looks like you have effectively zoomed in on the subject. Remember, this applies only to using the same lens on both cameras. The 17-50mm f/2.8 (APS-c only lens) was developed to counter this issue on APS-C sensors. It offers "equivalent" images that you would see with operating a 28-75mm f/2.8 on the Full Frame or 35mm-film body.

Hope that makes some sense. OMG ... it this horse dead, yet? We are so far off my topic ...

Last edited by DonSchap; 05-08-2011 at 09:41 PM.

Don Schap - BFA, Digital Photography A Photographer Is ForeverLook, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.flickr® & Sdi

the tammie shows its exceptional sharpness in that test, but hardly decent opposition. the sony 85/2.8 and rockinon are paperweights. both were just classic cases of "gear acquisition syndrome" and were poor decisions. so lets think about that $1369 CZ 85mm for a moment...and leave the tammie out of this cos its a great lens in its own right.

rokinon - $250
sony/2.8 - $250
sigma - $969

a grand total of $1469 if my math is right.

you could have had just 1 superb lens plus $100 spending money rather than 2 crap lens' and one decent one. hopefully the less experienced users learn from these mistakes. buy once and buy right. i'm also willing to bet that within a year the CZ85mm will be in your bag.

i can recall this very same conversation quite a few times in the past. lol

Don, you'd have to admit that Rooz has a point although there is a good case for having both the macro and the 85mm.
I've often said that if you can afford the best, and you obviously can, then that's what you should buy.
Just think, you could have been using the Zeiss since you bought the A900 rather than mucking around with these others.

And why would you need to know.
For those of use who spent years with FF (Full Frame) film cameras, the coming of digital crop cameras meant that our perception of focal length had to change.
That is to say that our 50mm 'normal' lens appears to be a 75mm on the Sony camera. Note that the focal length is the same, all that has changed is the FOV (Field Of View).
BTW, that multiplier only applies to Sony, other makes have different multipliers.

But, as a newcomer to photography and straight to a crop camera, you don't need to know that. Just get used to the different focal lengths on your camera, time enough to worry about it if you ever graduate to a FF camera.

Just know that a Wide angle lens is anything less than say 20mm, a normal lens is 33mm and short telephoto is 40-60mm. These are approximations.

And why would you need to know.
For those of use who spent years with FF (Full Frame) film cameras, the coming of digital crop cameras meant that our perception of focal length had to change.
That is to say that our 50mm 'normal' lens appears to be a 75mm on the Sony camera. Note that the focal length is the same, all that has changed is the FOV (Field Of View).
BTW, that multiplier only applies to Sony, other makes have different multipliers.

But, as a newcomer to photography and straight to a crop camera, you don't need to know that. Just get used to the different focal lengths on your camera, time enough to worry about it if you ever graduate to a FF camera.

Just know that a Wide angle lens is anything less than say 20mm, a normal lens is 33mm and short telephoto is 40-60mm. These are approximations.

You're right, Peter. I do not know why I even spent a moment on explaining the nuances of Full Frame to APS-C. LOL It is a total blow-off of knowledge.

Thank you for clearing that up. Until next time.

Don Schap - BFA, Digital Photography A Photographer Is ForeverLook, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.flickr® & Sdi